Most of us are quite familiar with what traditional braces look like. But occasionally we see more complex-looking devices being worn by young orthodontic patients: thicker wires that extend outside the mouth, with straps that may go behind the neck or over the chin. What are these devices, and why are they sometimes needed?

In general, orthodontic appliances with external parts braced by the head, neck or chin are referred to as “headgear.” These devices may be used to handle a number of particular orthodontic situations, but they all have one thing in common: They provide the additional anchorage needed to move teeth into better positions.

It may come as a surprise that teeth, which seem so solid, can actually be moved fairly easily over time. This is because teeth are not fixed directly into bone, but are instead held in place by a hammock-like structure called the periodontal ligament. Using a light, controlled force — such as the force of springy wires and elastics in traditional braces — teeth can be moved slowly through the jaw bone, like a stick being pulled through sand.

Of course, to pull a stick through sand, you need a firm anchorage — your legs, for example, bracing against a rock. Most of the time, the back teeth, with their large, multiple roots, provide plenty of support. But sometimes, the back teeth alone aren’t enough to do the job.

If a very large space between teeth is being closed, for example, the back teeth might be pulled forward as the front teeth are pulled back; this could result in poor alignment and bite problems. In other cases, the front teeth may need to be pulled forward instead of back. The back teeth can’t help here; this is a job for headgear.

Some types of headgear have a strap that goes behind the head or neck; they use the entire head as an anchorage. Other types, called “reverse pull” headgear, have a strap that comes over the chin or the forehead; they can pull teeth forward. Headgear can even influence the proper growth of facial structures — that’s why it is usually seen on preteens, whose growth isn’t yet complete.

Headgear is usually worn for 12 hours per day, for a limited period of time. In some cases, rather than headgear, appliances called “temporary anchorage devices” (TADS) may be recommended. These are tiny screws that are implanted into the jawbone in a minimally invasive procedure, and serve a similar function.

While it may not look pretty, orthodontic headgear is capable of moving teeth into their proper positions in a relatively short period of time — and ending up with a great-looking smile is what orthodontics is all about.